There are numerous articles, studies and patents pertaining to reduction or removal of sulfur dioxide and nitrogen oxides in boiler stack gas. However, sulfur dioxide and nitrogen oxides are not being removed from most boiler stacks in industry because of costs involved and difficulty of installation of usual equipment. We have reviewed all of the following patents:
______________________________________ Patent No. Inventor Date ______________________________________ 4,690,807 A. Saleem 9/1/1987 4,474,740 H. Karwat, et al 10/2/1984 4,590,048 A. Spitz 5/20/1986 4,248,842 K. Kaupisch, et al 2/3/1981 4,753,784 D. C. Neuerman 6/29/1988 4,565,678 Clyde W. Zielke, et al 1/21/1986 4,268,489 Egor Huese 5/19/1981 ______________________________________
None of these fulfill the major objective of the present invention which is to provide an economical method for sulfur dioxide removal and nitrogen oxide reduction in boiler stack gas. The objective may be realized by scrubbing with ammonium sulfite for sulfur dioxide removal and using chelated iron and ammonia for nitrogen oxide reduction. The method is economical because:
1. use of an engineering design to allow retrofitting installed boiler stacks to act as scrubbers;
2. using a cooling pond for ammonium sulfite oxidation, staok gas cooling, and storage of approximately 50% ammonium sulfate solution that is formed;
3. the chelated iron used for nitrogen oxide reduction is a most desireable addition to the ammonium sulfate-ammonia nitrate fertilizer mixture that is formed; Fertilizers currently sold with chelated iron command a premium price;
4. cooling pond storage allows ammonium sulfate to precipitate during a time of low fertilizer sales and be redissolved during high sales period. The 50% solution could also be evaporated to dryness with the ammonium sulfate bagged for sale; however, relatively local sale as a 50% solution would probably be more economically desireable. Local sale or sale within a 50 mile radius is probable since our calculations indicate that when burning 2% sulfur cool in a 600,000 pph boiler that ammonium sulfate and nitrate mixture is only approximately 96 tons/day. A cooling pond of two to three acres would hold a years production at normal depths but a larger area may be necessary for cooling.